1. Field of the Invention
The present invention relates to a method of accounting for technical uncertainties, while keeping the underlying physical reality, and rapidly, in an oil reservoir providing an economic profitability study.
2. Description of the Prior Art
According to the prior art, in the petroleum industry, an economic reservoir profitability study is generally based on production profiles determined beforehand. Determination of several oil production profiles, i.e. the evolution of the reservoir production in the course of time, is carried out by selecting several possible scenarios, for example highly likely, likely and unlikely, related to the uncertain technical parameters of the reservoir. Production of a reservoir in the course of time is defined by the evolution of its fluid production in the course of time. It can be, for example, the evolution with time of the oil and/or gas and/or water production of the reservoir. Oil production scenarios are established by means of a reservoir flow simulation software. The economic profitability study is then performed on uncertain economic parameters for each scenario. The scenario method is used so as to limit the number of flow simulations, costly in calculating time, that are required for the economic profitability study.
For each scenario, the method according to the prior art allows obtaining the uncertainties associated with the economic profitability of the reservoir (net present value, internal rate of return, etc.) by defining probability densities associated with the uncertain economic parameters, then using Monte Carlo type methods. This method thus allows determining the uncertainty on the economic profitability of a reservoir due to economic parameters for previously determined and fixed production scenarios which are a function of the uncertain technical parameters related to the reservoir.
However, the methods according to the prior art present inadequacies due notably to the fact that the impact of each technical parameter on the economic profitability of the reservoir is not taken into account directly and explicitly. In fact, the technical parameters are taken into account globally in the definition of the production scenarios (established by numerical flow simulation), which include all the uncertain technical parameters. It is therefore not possible, for example, to quantify the impact of a given uncertain technical parameter (aquifer activity, porosity, permeability, etc.) on the economic profitability of the reservoir or to optimize the position of a well in order to maximize this profitability. In general terms, with the methods of the prior art, it is not possible to rapidly and systematically carry out risk studies about the economic profitability of a reservoir by integrating directly the economic as well as the technical uncertain parameters.